Method of making frosted bulbs



Patented Nov. 22, 1938 PATENT OFFICE 2,137,683 METHOD OF MAKING FROSTED BULBS James" J. Flaherty, Newark, N. J.,

assignor to Wabash Appliance Corporation, Brooklyn, N. Y., a corporation of New York No Drawing. Application July 28, 1937,

I Serial No. 156,090

3 Claims.

This invention relates to frosted bulbs, and more particularly to the bulbs of the character that are employed in the fabrication of completed incandescent lamps, although it will be readily 5 understood that the invention is not necessarily limited thereto. Moreover, the invention is particularly directed to frosting the interior surfaces of such bulbs.

One type of curved glass to which my invention is particularly applicable is the inside or concave surface of glass bulbs,- such as are used in the fabrication of incandescent lamps. With the increase in efficiency and brilliancy of incandescent filaments, as well as the concentration thereof to small linear dimensions, it has become necessary to adopt means to eliminate or diminish the glare resulting therefrom. It has been common practice to etch, as by sandblasting or chemically, the surface of the glass to give to it a milky appearance, known in the art as frost. The method of etching the glass has likewise been known as frosting.

Lamp bulbs frosted on the outside are subject to the disadvantage of collecting dust, dirt, and the like, necessitating their frequent washing. Lamps heretofore frosted on the inside have been subject to the disadvantage of decreasing the strength of the glass. Thus, while it has been known for many years (for example in Kennedy Patent No.

733,972 of 1903) that incandescent lamps could be frosted on the inside, for example by a chemical etching solution, inasmuch as this frosting was effected by eating away some of the glass with the resulting lessening in strength of the glass, insufiicient strength remained to permit the commercial utilization of the principle of frosting the inside of the glass bulbs. It was thereafter announced that as a result of the discovery shown and described in Pipkin Patent No. 1,687,510,

issued October 16, 1928, on an application filed June 29, 1925, the inherent weakening of a lamp bulb incident to frosting the inside thereof by a single etching application could be overcome at least to an extent permitting commercial pro- 45 duction and utilization of inside frosted lamps if two or more applications of the etching solution were made. The theory was that the first application of the etching solution left sharp angular crevices on the surface of the glass which pro- 50 moted breakage, but repeated applications of etching solutions, preferably diluted in strength, would result in eating away the sharp angular crevices and, in eifect, rounding out the depressions initially formed, thereby reducing the tend- 55 ency to break and enabling the retention of strength in excess of 45% of that of the clear, unetched bulb.

The disadvantages of the so-called "multiple shot etching process, of which that of the Pipkin patent is illustrative, remain. In the first place, 5

it is obvious that the necessitated repeated operations of the production of the inside frosted bulb proportionately increases the expense of production. In the next place, repeated etchings result in an extremely fine etching producing a light bulb. Of course a darker bulb, produced by a coarser etching, is far preferable in use because the light absorption is less and the efliciency of the lamp is increased.

It is among the special purposes of my present invention to produce a bulb suitable for use, for example, as the bulb of an incandescent lamp, which is frosted on the inside by a single etching step wherein a coarse etching eifect, and in consequence a dark bulb, is obtained; but wherein the strength of the bulb is in excess of from 20 to 45% of the strength of the corresponding clear, unetched bulb, e. g. is strong or stronger than the bulb used commercially today, assertedly obtained by a multiple shot etching process.

I have discovered that when glass is subjected to the action of an etching solution within predetermined limits of certain concentrations at certain temperatures and for a certain period of time a substantial coating of the glass is effected. I have also found that in producing a strong inside frosted bulb by the one-shot process of myinvention that whenever this coating occurred commercial strength of the bulb resulted; but if for' any reason a substantial coating was not effected the bulb would not attain adequate commerciai strength.

In determining the factors that produce the necessary coating in the coarse etched single shot process of my invention I ascertained that it depended upon three factors, namely-(1) the etching solution and its concentration; .(2) the temperature of either the etching solution or of the bulb while being etched; and (3) the time of etching. 45

As to the solution, it is at the present time standard practice to use an etching solution consisting of water 11.2%, ammonium bifiuoride 28.3%, hydrofluoric acid (60%), 35.7%, ammonium bicarbonate 17.7%, and soda ash 7.1% by weight. In accordance with my invention I depart from this standard concentration and use water 9.3%, ammonium bifluoride 23.4%, hydrofluoric acid (60%) 46.8%, ammonium bicarbonate 14.6%, and soda ash 5.9% by weight. There is of course reasonable flexibility as to the proportions of the above ingredients, particularly as to all thereof except the hydrofluoric acid. I

portant factor in producing, by a single shot process, a strong coarse etched dark bulb.

As to the temperature at which etching is effected, I found that approximately 47 C. for the etching solution is satisfactory. Due to the fact that it is dimcult to maintain a fairly constant temperature for the etching solution, one way of accomplishing the same result is to maintain constant the temperature of the water bath in which the etching solution tank is located while being etched at approximately 60 C.

Another way of accomplishing the same result and to obtain the proper temperature is to .heat the bulb itself prior to etching it, in which event the temperature of the water bath can be proportionately lowered, or if the temperature controlled etching solution is used it can likewise be proportionately lowered.

As is obvious, the temperature is reasonably flexible but I have found that the best results have been obtained when an etching solution of approximately 47 C. has been used.

With respect to the time of treatment, the time, as used by me herein, includes the time from the introduction of the etching solution to the time the etching solution is washed out of the bulb. I have found that with the concentrated solution and the temperature treatment above described the proper time of etching is in the order of one minute.

Inasmuch as the ultimate product, viz: the inside frosted bulb, is dependent upon all three factors reasonable flexibility of any of the three may be had, provided it is compensated for in the other two. Thus, for, example, a less concentrated solution can be used with a longer period of time for etching. This flexibility of treatment lends itself particularly for factory utilization.

My invention is not concerned with the apparatus utilized in the commercial frosting of the inside of the bulbs, and any apparatus now in use or suitable therefor may be employed. Of

course thebulbs are subjected to the etching solution of the proper concentration and at the proper temperature and for the proper period of time as herein .set forth. The bulbs are then washed out so as to remove the etching solution and the coating which has formed, all in accordance with standard practice.

As hereinbefore stated, the resulting strength of the frosted bulb seems to depend upon the degree of coating eiTected on the glass wall as a result of the etching. I am unable to advance a theory as to what causes this particular coating, but I have definitely established that when it does occur in a suflicient amount, as it will when the treatment of my invention is employed, commercial strength for an inside frosted dark bulb is obtained.

Having now set forth the objects and nature of my invention, and having described the features thereof, what I claim as new and useful and of my own invention and desire to secure by Letters Patent is: 1. The method of producing an inside frosted glass bulb which consists in subjecting the interior surface of a glass bulb to an etching solution including water, ammonium bifluoride, ammonium carbonate, soda ash and a 60% solution of hydrofluoric acid in excess of 40% by weight for less than two minutes at a temperature of about 47 C.

2. The method of producing an inside frosted glass bulb which consistsin subjecting the interior surface of a glass bulb to an,etching solution including in approximately the following proportions, by weight, water 9.3%, ammonium bifluoride 23.4%, a 60% solution of hydrofluoric acid in excess of 40%, ammonium bicarbonate 14.6%, and soda ash 5.9%, for less than two minutes at a temperature of about 47 C.

3. The method of producing an inside frosted glass bulb which consists in subjecting the interior surface of a glass bulb to an etching solution including in approximately the following proportions, by weight, water 9.3%, ammonium bifluoride 23.4%, a 60% solution of hydrofluoric acid 46.8%, ammonium bicarbonate 14.6%, and soda ash 5.9%, for less than two minutes at a temperature of about 47 C.

JAMES J. FLAHERTY. 

